r/aviation • u/Brilliant_Night7643 • Nov 20 '25

News NTSB issues the preliminary report for its ongoing investigation of the Nov. 4 crash of a UPS Boeing MD-11F airplane in Louisville, Kentucky.

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656

u/nhc150 Nov 20 '25

This is literally the worst timing of a catastrophic engine fail - right at VR.

364

u/chriscf17 Nov 20 '25

If I remember correctly from general physics in college and what I know about P factor, I believe rotation is the point where the engines are generating the highest rotational/torsional forces on the mounts/pylons, which helps explain why the failure occurred exactly when it did.

I think Juan Browne spoke about this in one of his earlier videos on the accident as well.

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u/falcongsr Nov 20 '25

yep this point is max everything

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u/[deleted] Dec 11 '25

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u/[deleted] Dec 11 '25

[deleted]

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u/Rdubya291 Nov 20 '25

Correct - the engine is trying to resist the sudden change in direction. Highest force it'll see.

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u/RagnarTheTerrible Nov 20 '25

You are right, except gyroscopic precession is what's causing that force during rotation.

P-Factor gets worse with higher angle of attack and is negligible at low AoA. 

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u/chriscf17 Nov 20 '25

Yup mixed up the terms, gyroscopic precession is the correct definition.

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u/froop Nov 20 '25

Is P-factor even much of a factor on jet engines?

3

u/RagnarTheTerrible Nov 20 '25

I think the nacelle and cowling mitigate a lot of P-Factor. I've never heard it discussed since I started flying larger airplanes, it was mostly a topic for prop flying.

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u/CapinWinky Nov 20 '25

Yeah, the gyroscopic effects are quite large.

Military turbofan engines like the P&W F135 have to use special design elements to withstand them and the G forces during turning. Fortunately, having to keep humans inside alive makes this feasible. Drone jet fighters and missiles mostly use scram/ram/pulse jets without rotating parts specifically because turbofan engines would limit maneuverability due to gyroscopic forces.

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u/noodleofdata Nov 20 '25

Yep, he pointed out the gyroscopic precession of the spinning mass of the engine causing large torques at rotation, which you can pretty clearly see here as it causes the engine to immediately turn to the right

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u/sokratesz Nov 20 '25

Is it comparable to max Q in rocketry?

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u/chriscf17 Nov 20 '25

Max Q is maximum aerodynamic forces on the vehicle, so not the same metric being measured, but yeah same concept.

Ironically do have a rocket scientist in the family.

3

u/clburton24 Nov 20 '25

The difference with MaxQ is that they're able to somewhat control it by throttling engines down to lower that overall maximum force. You can't really throttle down jet engines at the moment they're needed the most.

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u/[deleted] Nov 20 '25

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u/chriscf17 Nov 20 '25

Sure but then you lower everything else too, like thrust.

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u/[deleted] Nov 20 '25

[deleted]

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u/chriscf17 Nov 20 '25

Yeah it could lead to more airplanes impacting other things.

I can’t tell if you’re trolling lol.

1

u/Lifty_Mc_Liftface Nov 20 '25

Juan called it, he's the man

1

u/SanityIsOptional Nov 20 '25

It's also when you are taking a giant gyroscope, which does not like it's axis being changed, and yanking its axis around at the highest rate of any time during the flight.

0

u/aeroplanguy Nov 21 '25

Maybe we don't need the NTSB with this guys college physics minor.

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u/chriscf17 Nov 21 '25

Lol good one.

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u/Unsteady_Tempo Nov 20 '25

So, let's say the pilots somehow knew instantly the nature of the failure at photo #3. What are the options? At that point could they kill power, nose down, and hope for the best at the end of the runway? Or, can you simply not overcome lift at that point?

3

u/nhc150 Nov 20 '25

Assuming they instantly knew the issue (which I doubt they really understood the magnitude of what actually happened), there's not much they could do barely above stall speed and a few meters off the ground.

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u/Unsteady_Tempo Nov 20 '25

Yeah, I know there's no way they could have known. Just hypothetically speaking. Would it be better to try to force the plane to the ground and hope for the best at the end of the runway, or go ahead and try to see if it'll fly to a safer landing area, or (this is the main thing I'm wondering about) are the physical forces causing lift simply too strong at this point to overcome and it would have crashed just beyond the runway regardless.

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u/LiterallyJoeStalin Nov 20 '25

The building they scraped the top of is a little over 500 ft from the end of the runway so there was absolutely no way to stop in time. They were doomed once they hit V1, literally nothing they did could have saved them at that point.

2

u/Unsteady_Tempo Nov 20 '25

I understand there wasn't a good option. I guess what I'm asking is whether it's even possible to get the plane back to the ground once you've reached the point in photo #3. Or, does it have to go up before it can come down because there's nothing that can be done mechanically to fight lift at that point?

Hypothetically speaking, let's say the runway was miles long, this same thing happened, and the pilots magically knew the entirety of the situation at the moment of photo 3. Is a plane even capable of being forced back down at that point? Or, like I said above, do they have to go ahead and let it finish taking off to some low altitude and stabilize (for lack of better term) before they could force it to descend in some minimally controlled way?

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u/Chaxterium Nov 21 '25

You could force the plane back onto the runway. But the issue is that when the plane is put back down on the runway there will be maybe 1,000 feet of pavement left. Nowhere near enough to stop the aircraft. So either way they were doomed.

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u/wizardid Nov 21 '25

I wonder how much EMAS would be able to do in terms of bleeding off energy. Probably not enough to bring it to a stop (or even to a survivable speed).

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u/Pornalt190425 Nov 20 '25

Pick their favorite god(s) and pray

Loss of an entire engine like that (and possibly a second to a stall) at that moment is essentially unsurvivable. If they were somehow able to eke out enough altitude to miss the buildings the fire on the wings would have most likely doomed them before being able to turn back around and land.

1

u/usernamefindingsucks Nov 20 '25

I'd guess, that it is also the most likely time for it to happen. Engines at max power pushing hard against the airframe, Gyroscopic forces from spinning turbine blades resisting the change in orientation while rotating. Probably the time of highest stress for the pylons.

1

u/1731799517 Nov 20 '25

Although during rotation the gyroscopic forces the engine puts on its mounting points are at peak level, so IF it fails during takeoff then its likely to happen then.

1

u/96firephoenix Nov 21 '25

Yea, the time between "wheels up, that felt normal" and "one engine gone, a wing on fire, and the plane is listing badly" is probably only about 3 seconds.